Originally Posted by
megan
tdracer, perhaps you are in a position to confirm that the only similarity between the two aircraft is that they look similar. Have seen it written that structure is even built of a different grade metal, reflecting the difference between commercial and military requirements.
My memory is a bit fuzzy on the subject, but I'll try
.
I do know it's a popular myth that the 707 is just a civilian version of the KC-135 and that gave Boeing a big commercial advantage in that the USAF paid for the 707 development - the reality is far more complex. The KC-135 derived directly from the "Dash 80" prototype - which Boeing developed on their own, paid for out of Boeing's pocket. The cost of the Dash 80 development was more than the net worth of Boeing at the time - hence the line "they bet the company" on the Dash 80 was literally true - but it worked and the USAF launched the KC-135 program.
At about the same time Boeing launched the 707, Douglas launched the DC-8 - which had a wide enough fuselage for six across seating - something the Dash 80/KC-135 didn't allow. So Boeing completely changed to fuselage to also allow six abreast seating. The flight deck layout was different on the 707 - the wing layout and structure was pretty much the same, and the original engines were pretty much the same. But that was only for very first 707s. Things were evolving quickly, and by the time they got to the turbofan powered 707-320 (the most common version), there were very few parts common with the KC-135 - even the wing shape was different.